1. Field of the Invention
The invention relates generally to systems, devices and methods for disengaging and engaging a wrap spring clutch. More particularly, the invention relates to actuators for a spring wrap clutch used in agricultural row crop planters.
2. Description of the Related Art
The seed delivery mechanisms used on row crop planters are commonly powered from a single source. This source may be a ground-driven tire and transmission combination that maintains a seeding rate regardless of travel speed or a powered drive such as a hydraulic drive system that uses sensors to measure the travel speed and a central control unit that causes the motor to turn at the correct rate to plant at the desired seeding rate.
In either case, individual control of seed meters is not possible. All of the seeding units powered by the drive mechanism are planting, or all of the seeding units are not planting. Various methods evolved to provide some level of control over the seeding mechanisms on groups of individual rows and ultimately individual rows.
One of the most common ways to control individual rows or groups of rows is with a mechanical clutch. One of the most commonly used mechanical clutches is a wrap spring clutch. With such a clutch, a small amount of power can be used to instantly engage, hold, and disengage the rotating mechanisms used to singulate the seeds and deposit them in the furrow. Wrap spring clutches use a pair of hubs or drive shafts, an uncontrolled input drive shaft in operative connection with a first clutch plate and an output drive shaft in operative connection with a second clutch plate. A torsion spring is compressed against and wrapped around a portion of the first and second clutch plates, the torsion wrap spring comprising an actuable tang positioned radially outwardly from the wrapped torsion spring. The tang may be engaged in a release collar. Rotating power supplied to the input drive shaft causes the spring to wrap tightly around the first clutch plate to the second clutch plate through friction. If an obstacle stops the rotation of the release collar, the tang is actuated, stops rotating and the spring consequently unwinds, releasing the friction between the spring and the first clutch plate. When this occurs, the input drive shaft and first clutch plate rotate freely while the wrap spring, second clutch plate and output drive shaft cease rotating. When the obstacle is removed from the release collar, disengaging the tang, the spring begins to wind, rotating with the input drive shaft and first clutch plate, friction increases rapidly until the second clutch plate and output drive shaft are rotating with the first clutch plate and input drive shaft as a single unit.
Typically, clutches are actuated either mechanically, pneumatically, e.g., with a compressed air cylinder, electrically, e.g., with a solenoid or the like. In some systems, particularly low current systems, the amount of current required to actuate the clutch limits the number of clutches that may be incorporated into the system. In both the systems using an electrical solenoid or a compressed air cylinder, a force is applied in one direction and a return spring creates the opposing force to cause the clutch mechanism to return to its normal state. This requires the actuating device to move with sufficient force to engage the tang by, e.g., stopping the release collar, and overcoming the return spring. The return spring must have enough compressed force to overcome friction and move the actuator away from the release collar. Large amounts of electrical power or compressed air are required to ensure consistent operation of the device.
For example, for a typical planter, a solenoid requires approximately 30 amps to pull a piston to engage a release ring, and approximately 1 amp to hold the piston in engagement. Consequently, because the electrically system is limited in capacity, one clutch is used to activate several corn planter assemblies.
Early planters placed such actuation devices in a common place on the driveline of the planter so that, when actuated, planting activity would cease on ½, ⅓ or ¼ of the whole machine. A single clutch controlled a group of rows. In this application, power demand was not a concern as only one or two clutch mechanisms were powered at a time. Later, as Global Positioning System (“GPS”) control became more common, seed costs began rising and farming practices changed, the demand to place a clutch on each row became more common. Power usage became a concern.
The accuracy of GPS control of individual row clutches became a concern. Typical agricultural systems used in this application may not have the ability to start and stop individual rows accurately. For example, an outside row may be planting 30 inches from a previous planting pass. If the machine drifts too closely to the previous planting pass, then the GPS control system may interpret its information to conclude this row unit has passed into previously planted area and cause it to stop dropping seeds. This results in an unwanted skip in the row.
To overcome this problem, most planters have the individual row clutches tied together in groups of 2, 3 or more. When the GPS control unit sends the signal to disengage the drive, all the row units in that group stop planting at the same time. This moves the distance from pass to pass farther away, preventing unwanted shutoff, but it can also result in less than perfect operation in other aspects and circumstances. For example, consider the case where a group of 3 row units are tied to the same control signal and clutch mechanism. If this group enters a previously planted area at, e.g., an acute angle, one row will stop planting too early leaving an unplanted portion of the row, one row unit will stop at the correct place in the row and the third row unite will continue to plant into the previously planted area, thereby wasting seed and reducing yields from over population.
The present invention overcomes these deficiencies.